1. Field of the Invention
The present invention relates to a specified resin composition which comprises a crystalline propylene-ethylene block copolymer, an ethylene-.alpha.-olefin copolymer and talc, which has an excellent balance between low-temperature impact resistance and rigidity, and which is suitable for producing injection molded products such as automobile interior and exterior trim parts, e.g., instrument panels, bumpers, etc.
2. Description of the Related Art
Although crystalline polypropylene has excellent characteristics such as rigidity, heat resistance and gloss, it has the drawback that it cannot be used for applications which simultaneously require good rigidity, heat resistance, impact resistance and coating properties because it exhibits poor impact resistance and coating properties. Particularly, since crystalline polypropylene has poor impact resistance at low temperatures, the application thereof to automobile exterior trim parts such as bumpers is limited. A method for overcoming such drawbacks is proposed in which a rubber component such as an amorphous ethylene-propylene copolymer is mixed with the crystalline polypropylene. A method of adding and mixing an inorganic filler such as talc or the like is also proposed for preventing loss of rigidity by the addition of such rubber substances.
For example, Japanese Patent Publication No. 60-3420 discloses a polypropylene composition for automobile bumpers, which contains 55 to 65% by weight of crystalline propylene-ethylene block copolymer having an ethylene content of 5 to 10% by weight, at least 97% by weight of the component of polypropylene insoluble to boiling n-heptane, an intrinsic viscosity (decalin at 135.degree. C.) of room temperature para-xylene soluble matter of 3 to 4 and a melt flow index of 2 to 10; 30 to 35% by weight of amorphous ethylene-propylene copolymer having an intrinsic viscosity (decalin at 135.degree. C.) of 2.0 to 3.5 and a Mooney viscosity ML.sub.1+4 (100.degree. C.) of 40 to 100; and 5 to 15% by weight of talc having an average particle size of 0.5 to 5.mu..
Japanese Patent Publication Nos. 63-42929 and 4-28749 disclose polypropylene compositions which contain an ethylene-.alpha.-olefin copolymer as a material for improving impact strength in place of an amorphous ethylene-propylene copolymer, but this composition does not always have a satisfactory balance between low-temperature impact resistance and rigidity.
Japanese Patent Laid-Open No. 4-159345 discloses a polypropylene composition in which the melt flow rate is 4 to 50 g/10 min., the density is 0.910 g/cm.sup.3 or less, the highest melting peak temperature measured by a differential scanning calorimeter (DSC) is at least 100.degree. C., and the highest melting peak temperature again as measured by DSC of an ethylene-.alpha.-olefin copolymer having melting heat of at least 10 joule/g at at least 100.degree. C. is as high as 100.degree. C. or more. Thus the polypropylene composition does not always have satisfactory impact resistance.